Sound reproduction apparatus



United States Patent lC 3,145,265 SOUND REPRODUCTIUN APPARATUS Yoshiaki Tamara, 2112 February Court, George W. Carmichael, 936i) Lavell St., and Panes l). Georgantas, 2924 Juniper t., all of San Diego, Calif.

Filed Apr. 10, 1961, der. No. 101,810 4 (Ilaims. (Cl. 179--1) The present invention relates to sound reproduction apparatus, and more particularly to sound reproduction apparatus which is adapted to provide a stereophonic sound effect.

According to the present invention, monaural or single channel sound is converted by a system having two sound channels, one channel provided with a time delay, to thereby provide an apparent stereophonic sound effect. The listener perceives the sound omnidirectionally. That is, in contrast to conventional stereophonic systems utilizing more than one channel as a sound source, the apparent stereophonic sound resulting from the utilization of the present apparatus appears to reach the listener from a great multiplicity of paths, and there is no apparent localization of the sound source. More particularly, with a conventional stereophonic system, the listener is aware of the direction of each sound source if he is not located in a predetermined position with respect to the various loudspeaker outputs. If the listener moves to one side the speaker on that side dominates the associated speaker, and if he moves to the other side the speaker on that side has a similar effect. In contrast, the stereophonic effect produced by the present apparatus is apparently omnidirectional in the room in which the listener is located.

This apparent stereophonic effect is produced in the present invention by providing a time delay in a secondary sound reproducing channel whose signal source is a primary sound producing channel, both of these channels then driving a pair of output loudspeakers. That is, a monaural or single track source of audio-frequency elec trical signals is employed to drive a first output loudspeaker, which is the speaker of the primary channel. A portion of this single track signal is tapped oil and fed through an acoustical time delay, and thence to a second output loudspeaker, which is the speaker of the second or auxiliary channel. The sound from the second output loudspeaker is delayed from that of the first output loudspeaker, and thus the listener is provided with the illusion of hearing sounds traveling through acoustic paths of different lengths. Thus, the present apparatus is not a conventional stereophonic system in the sense of employing channels requiring two or more separate sound sources, but is instead characterized by a single sound source.

The apparatus of the present invention may be employed to provide a pseudo-stereophonic effect by using any one of a number of sources for audio-frequency electrical signals, such as AM. or FM. radio transmissions, phonograph records, tape or wire records, and the like.

The acoustical delay apparatus of the present invention includes a pair of conventional loudspeakers, hereinafter sometimes referred to as acoustical delay speakers, arranged in axial, confronting relation within an enclosure, and the tapped off signal from the audio source is applied to the leads of the voice coil of one of the acoustical delay speakers, and the resulting acoustical vibrations are transmitted through the fluid medium of the enclosure toward the other acoustical delay speaker, exciting said other speaker which, in turn, converts the excitations into audiofrequency electrical signals which are then amplified and fed to the second output loudspeaker. In effect, the pair of opposed, confronting acoustical delay loudspeakers in the enclosure divides the enclosure into three fluid columns, one of these columns serving to backload one of the acoustical delay loudspeakers, another of the fluid 3,145,265 Patented Aug. 18, 1964 and columns serving to backload the other acoustical delay speaker, and the third fluid column between the two acoustical delay speakers serving to transmit the acoustical vibrations from one of the acoustical delay loudspeakers to the other of the acoustical delay loudspeakers.

It has been found that this type of acoustic delay is not subject to acoustic feedback, that is, the sounds generated by the output loudspeakers of this system do not affect the character of the signals emanating from the acoustic delay loudspeakers. This is in sharp contrast to the undesirable effects which would be produced were a microphone or other similar form of pick up used in the acoustic delay system. Further, inasmuch as the two acoustic delay loudspeakers are not subject to acoustic feedback, the insulation of the enclosure within which the acoustical delay loudspeakers are mounted is not critical.

It is, therefore, an object of the present invention to provide an apparatus which is adapted to convert a monaural or single track source of sound into apparent stereophonic sound by utilizing a portion of the audiofrequency input electrical signals to drive one output loudspeaker, tapping off another portion of the audio-frequen cy input signals, delaying this latter tapped 0d portion in an acoustic delay apparatus, and applying the output of the acoustic delay apparatus to a second output loudspeaker.

It is another object of the present invention to provide an acoustic delay apparatus consisting of a pair of confronting, axially aligned electro-acoustic transducers or loudspeakers in an enclosure to define three fiuid columns, one for ,backloading one of the loudspeakers, another for backloading the other of the loudspeakers, and the third for transmitting the acoustical vibrations of one of the loudspeakers to the other of the loudspeakers to thereby obtain the desired delay.

It is a further object of the invention to provide an acoustic delay apparatus in an audio reproduction system, which acoustic delay apparatus is relatively inexpensive, easy to construct, and wherein the acoustic insulation is not critical.

It is still another object of the invention to provide an acoustic delay apparatus which is substantially not susceptible to acoustic feedback.

It is also an object of the invention to provide audio reproduction apparatus for creating a pseudo-stereophonic or binaural effect while using only a single track or monaural source of audio-frequency electrical signals, such as, for example, an A.M. or FM. radio transmission, a phonograph, a tape or wire recorder, or single track sound film equipment.

Other objects and features of the invention will become apparent from consideration of the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the apparatus of the present invention;

FIG. 2 is a wiring diagram of the acoustical delay apparatus of FIG. 1; and

FIG. 3 is a longitudinal cross-sectional view taken through the enclosure and illustrating the arrangement of the components illustrated diagramatically in FIG. 2.

Referring now to the drawing, and particularly to FIG. 1, there is illustrated an audio reproduction system for providing a stereophonic sound effect, and utilizing a monaural or single channel source 10 for the achievement of this effect. This monaural source may be a radio or television receiver or a tuner-amplifier combination whose output reproduces either A.M. or PM. transmission, a phonograph, a tape or wire recorder, or single track sound film equipment.

The monaural source 16 is coupled to a first output speaker 12 through a signal transmitting path M which includes a conventional amplifier l5, and a portion of the audio-frequency electrical signals in path 14 is tapped oil through a signal transmitting path 16 to an acoustical delay apparatus 13. As will hereafter be described in greater detail, the acoustical delay apparatus 18 introduces a time delay in the audio-frequency signals tapped off from the transmitting path 14. The output of the acoustical delay 13 is coupled to a usual and conventional amplifier 29, which amplifies the attenuated signal of the acoustic delay 1%, and thence the signal is fed to a second output loudspeaker 24. The signal level of the second output speaker 24 may be matched to that of the first output speaker 12 by adjusting the usual volume control of the amplifier 2%, the desired frequency response being achieved by adjustment of the usual tone control of amplifier Tell.

It will be seen from the diagram of FIG. 1 that only a single monaural channel or source is employed, the stereophonic effect produced by the present apparatus being achieved without utilizing the dual channels characteristic of conventional stereophonic system.

Referring now to FIG. 2, the audio-frequency electrical signals of the signal transmitting path 16 are applied to the acoustical delay 1% through a pair of leads as and 28 which are coupled to the secondary of the output transformer of the amplifier 15. These leads are connected to the input terminals of the voice coil 39 of an electroacoustic transducer or loud-speaker 32. The resulting acoustical vibrations produced by the first acoustical delay loudspeaker 32 excite an opposed or confronting, axially aligned, and preferably matching electroacoustic transducer or loudspeaker 34. The excitation of the second acoustical delay loudspeaker 34 is converted into audiofrequency electrical signals which pass from the voice coil 36 of the loudspeaker 34 to the input terminals of a stepup transformer 38. One of the output terminals of the transformer 38 is connected to a point of constant potential, indicated as a ground at 49, and the other output terminal of the transformer 3%; is coupled to the amplifier 20 and thence to the second output loudspeaker 24, as illustrated in FIG. 1.

Referring now to FIG. 3, the loudspeakers 32 and 34 are mounted in any suitable manner within an elongated, sealed enclosure 42, which may be made of half inch plywood or the like. The interior of the enclosure is preferably lined With acoustic insulation material 44, although the provision of the insulation 54 is not critical in the operation of the acoustical delay 18. in addition, the enclosure 42 need not be airtight, but should be sealed sufficiently to provide proper backloading, as will be apparent.

In one successful embodiment of the present invention, the loudspeakers 32 and 34 were four inch loudspeakers spaced approximately Vs inch apart, and disposed within a plywood enclosure 42 measuring 6 inches by 6 inches by 16 inches. Although it has been found that the space between the loudspeakers 32 and 34 is not extremely critical, a pleasing reverberation or pseudo-stereophonic effect is produced with the loudspeakers 32.. and 34 spaced apart approximately inch, as above-described, or even more closely positioned with the cones or diaphragms of the loudspeakers almost in mutual engagement about their peripheries.

It is to be noted that the location of the loudspeakers 32 and 34 within the sealed enclosure 42 is effective to define three fiuid columns, one in back of the loudspeaker 32, as at 46, one in back of the loudspeaker 34, as at id, and one between the loudspeakers as at d. The fluid column 46 is effective to backload the speaker 32., and the column 48 is effective to backload the speaker 34,, while the column St) between the loudspeaker is effective to transmit the acoustical vibrations which result from the application of the audio-frequency signals from the path 16 to the loudspeaker 32.

Although the speakers 32 and 34 can be positioned to provide fluid columns 46 and 48 of substantially equal length, they are preferably positioned to provide a column 46 greater in length than the column 48. This arrangement is preferred because the cone or diaphragm movements of the speaker 32, being the driver speaker, are appreciably greater than those of the speaker, 34, the driven speaker, and the backloading for the speaker 32 should, therefore, be provided by a larger volume, as by a column as larger than column 48.

It will be apparent that the medium within the enclosure 42 may be either a gas or a liquid, however, the sealing problems associated with the employment of a liquid medium would increase the cost and complexity of the unit, and, therefore, it is preferable to use an air medium.

Thus, a simple and effective means for introducing a time delay has been provided, and it has been found that the simulated or pseudostereophonic effect produced by the present apparatus is quite eilective. The cost of the components, the simplicity of their construction and assembly, and the ease of operation make the present apparatus inexpensive to manufacture. Also, the use of the loudspeakers 32 and 3 2- renders the present apparatus substantially unaffected by the audio output of either of the speakers 12 and 24 so that acoustic feedback is substantially eliminated. This is to be contrasted with the sensitivity of an acousti-electrical converter of sound, such as a microphone, which is highly sensitive to the sound generated by the output speakers of the sound system.

While the invention has been described by means of a specific example and in a specific embodiment, we do not wish to be limited thereto since obvious modifications and variations will occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. Acoustic delay apparatus for a sound reproduction system, said apparatus comprising: means defining an enclosure; a first loudspeaker and a second loudspeaker mounted in said enclosure in confronting, spaced relationship, said first and said second loudspeakers defining with said enclosure a first fluid column back of said first loudspeaker for backloading said first loudspeaker, a second fluid column back of said second loudspeaker for backloading said second loudspeaker, and a third fluid column between said first and said second loudspeaker for transmitting acoustical vibrations between said first and said second loudspeakers; means for applying audiofrequency electrical signals to one of said first and second loudspeakers; and means for transmitting audio-frequency electrical signals from the other of said first and said second loudspeakers.

2. In sound reproduction apparatus for providing a put of said first loudspeaker is directed toward and mechanically excites said second loudspeaker said first and said second loudspeakers defining with said enclosure a first fluid column back of said first loudspeaker for backloading said first loudspeaker, a second fluid column back of said second loudspeaker for backloading said second loudspeaker, and a third fluid column between said first and said second loudspeaker for transmitting acoustical vibrations between said first and said second loudspeakers. V

3. Acoustic delay apparatus for a sound reproduction system, said apparatus comprising: means defining an enclosure; a first loudspeaker and a second loudspeaker mounted in said enclosure in confronting, spaced relationship, said first and said second loudspeakers defining means!) with said enclosure a first fluid column back of said first loudspeaker for backloading said first loudspeaker, a second fluid column back of said second loudspeaker for backloading said second loudspeaker, and a third fluid column between said first and said second loudspeaker for transmitting acoustical vibrations between said first and said second loudspeakers, said first fluid column being of greater volume than that of said second fluid column; means for applying audio frequency electrical signals to one of said first and second loudspeakers; and means for transmitting audio-frequency electrical signals from the other of said first and said second loudspeakers.

4. Acoustic delay apparatus for a sound reproduction system, said apparatus comprising: means defining an enclosure; a first electro-acoustic transducer and a second electro-acoustic transducer mounted in said enclosure in confronting, spaced relationship, said first and said second electro-acoustic transducers defining with said enclosure a first fluid column back of said first electro-acous tic transducer for backloading said first electro-acoustic transducer, a second fluid column back of said second electro-acoustic transducer for backloading said second electro-acoustic transducer, and a third fluid column between said first and said second electro-acoustic transducers for transmitting acoustical vibrations between said first and said second electro-acoustic transducers; means for applying audio-frequency electrical signals to one of said first and second electro-acoustic transducers; and means for transmitting audio-frequency electrical signals from the other of said first and said second electro-acoustic transducers.

References Cited in the file of this patent UNITED STATES PATENTS 2,065,578 Glen Dec. 29, 1936 2,403,232 Parisier July 2, 1946 2,419,894 Hayes Apr. 29, 1947 2,832,843 Meissner Apr. 29, 1958 2,837,597 LuboW June 3, 1958 2,978,543 Kennedy Apr. 4, 1961 

1. ACOUSTIC DELAY APPARATUS FOR A SOUND REPRODUCTION SYSTEM, SAID APPARATUS COMPRISING: MEANS DEFINING AN ENCLOSURE; A FIRST LOUDSPEAKER AND A SECOND LOUDSPEAKER MOUNTED IN SAID ENCLOSURE IN CONFRONTING, SPACED RELATIONSHIP, SAID FIRST AND SAID SECOND LOUDSPEAKERS DEFINING WITH SAID ENCLOSURE A FIRST FLUID COLUMN BACK OF SAID FIRST LOUDSPEAKER FOR BACKLOADING SAID FIRST LOUDSPEAKER, A SECOND FLUID COLUMN BACK OF SAID SECOND LOUDSPEAKER FOR BACKLOADING SAID SECOND LOUDSPEAKER, AND A THIRD FLUID COLUMN BETWEEN SAID FIRST AND SAID SECOND LOUDSPEAKER FOR TRANSMITTING ACOUSTICAL VIBRATIONS BETWEEN SAID FIRST AND SAID SECOND LOUDSPEAKERS; MEANS FOR APPLYING AUDIOFREQUENCY ELECTRICAL SIGNALS TO ONE OF SAID FIRST AND SECOND LOUDSPEAKERS; AND MEANS FOR TRANSMITTING AUDIO-FREQUENCY ELECTRICAL SIGNALS FROM THE OTHER OF SAID FIRST AND SAID SECOND LOUDSPEAKERS. 